Inspirational Orbits - Astronomers are finding new planets

source: Scientific American, June 2009 by John Rennie, Editor-in-Chief

The year 1609 was noteworthy for two astronomical milestones. That was when Galileo built his first telescopes and began his meticulous study of the skies. Within months he discovered the four major satellites of Jupiter, saw that Venus (like our moon) has illuminated phases and confirmed earlier observations of sunspots—all evidence that undermined the Aristotelian model of an unchanging, Earth-centered cosmos.

During that same year, Johannes Kepler published Astronomia Nova, which contained his detailed calculation of the orbit of Mars. It also established the first two laws of planetary motion: that planets follow elliptical orbits, with the sun at one focus, and that planets sweep through equal areas of their orbits in a given interval.

Small wonder, then, that when the United Nations General Assembly declared an International Year of Astronomy to promote the wider appreciation of the science, it selected 2009, the quadricentennial of those standout accomplishments (among many) by Galileo and Kepler that informally founded modern astronomy.

Currently astronomers can look beyond the familiar planets and moons to entirely new systems of worlds around other stars. As I write this, the tally stands at 344 known extrasolar planets. Only a handful of these bodies were found by telescopic means that Galileo or Kepler would have recognized, but each one owes its discovery to their work. A recent and surprising trend is the apparent abundance of planets turning up close to very small stars—suns that may not be much larger than the planets circling them.

Astronomers Michael W. Werner and Michael A. Jura have more in their article starting on page 26, including why the existence of these unlikely planetary systems might imply that the universe is chockfull of planets.